Compression-bonded magnet with case and method for producing the same

ABSTRACT

There is provided a compression-bonded magnet with a case, which can realize high magnetic properties, high corrosion resistance and high durability strength even at low cost. The compression-bonded magnet with a case is a compression-bonded magnet with a case  1 , comprising: a compression-bonded magnet  2  comprising a rare earth magnet powder such as an isotropic Nd—Fe—B magnet powder and a resin binder of a thermosetting resin; a case  3  for inserting the compression-bonded magnet  2 ; and a sealing member  4 , wherein the compression-bonded magnet  2  is formed by compression-molding a mixture comprising the rare earth magnet powder and the resin binder into a green compact and curing the resin binder contained in the green compact, the rare earth magnet powder is contained in a large amount with respect to the entire compression-bonded magnet (for example, in a volume ratio of 85% to 90%), the sealing member  4  is fixed at an insertion opening part  3   a  of the case  3 , and the compression-bonded magnet  2  is hermetically sealed by the sealing member  4  and the case  3.

TECHNICAL FIELD

The present invention relates to a compression-bonded magnet with acase, for use in a sensor detecting the angle in a non-contact manner,and, particularly, to a compression-bonded magnet with a case, for usein a corrosive environment in which it is in contact with a fluid suchas water, oil or exhaustive gas and is required to have corrosionresistance, and to a method for producing the same.

BACKGROUND ART

Bonded magnets molded by binding magnet powders of a rare earth alloy bymeans of a resin binder contain the resin binder and thus have poorermagnetic properties than those of binderless sintered magnets, but areeasy to process into any shape and also excellent in dimensionalaccuracy, and therefore are used in various applications. For example,as regards their use in sensors detecting the angle in a non-contactmanner, bonded magnets are utilized as sensor magnets detecting theopening/closing angle in flow channel switching valves for water pumpsfor effectively cooling engines, inverters, batteries, etc. of HEVs andEVs, oil pumps, fuel pumps and the like in the automobile field, and areutilized as sensor magnets for detection of the absolute angle in robotsin the industrial machinery field.

Bonded magnets are classified into those obtained by charging a mixturecomprising a magnet powder and a resin binder such as a thermosettingepoxy resin into a mold for compression molding thereof(compression-bonded magnets) and those obtained by pelletizing a mixtureof a magnet powder and a thermoplastic resin binder andinjection-molding this pelletized mixture. Compression-bonded magnetscan contain a large amount of magnet powder as compared withinjection-molded magnets, and thus can attain high magnetic properties.

When rare earth magnet powders are used in bonded magnets, the magnetscontain iron or a rare earth element, and thus involve the problem ofinternal penetration of rust, or are likely to be deteriorated inmagnetic properties by oxidation corrosion. Especially, such problemsbecome pronounced in a corrosive environment in which the bonded magnetsare in contact with a fluid such as water. Therefore, in the bondedmagnet, a resin coating is formed on an exposed surface of the magnet,for example, by electrodeposition coating, electrostatic coating orspray coating to cope with the above problems.

Conventionally, there has been proposed a compression-bonded magnetproduction method in which a rust-proof thermosetting coating is formedon the surface of a rare earth magnet by an immersion method (see PatentDocument 1). This production method involves repeating a cycle ofimmersion, drying and curing twice to six times to form a rust-proofthermosetting coating with a size of 0.005 mm to 0.05 mm on the surfaceof a magnet while impregnating a resin into the voids formed in themagnet.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 2002-260943 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In recent years, small-sized sensors, which are used in an environmentin which they are in contact with a fluid such as water, oil orexhaustive gas and are required to have corrosion resistance, aredemanded to have higher magnetic properties while securing excellentcorrosion resistance and moldability. However, conventionalcompression-bonded magnets including one described in Patent Document 1can contain a large amount of a magnet powder as compared withinjection-molded magnets, but the amount of the magnet powder is at mostabout 83% in volume ratio with respect to the entire magnet. Themagnetic properties of this compression-bonded magnet may sometimes bedifficult to deal with the above requirement. There is a possibilitythat the durability strength of the magnet itself as acompression-molded body and the strength of adhesion, for example, to acase which holds the magnet cannot be maintained during use, simply bydecreasing the resin binder amount and increasing the magnet powderamount more than the normal limit amount (83%) in order to improve themagnetic properties.

On the other hand, it is conceivable to replace bonded magnets withbinderless magnets (sintered magnets) having higher magnetic properties.The binderless magnets, however, must be produced through the steps ofcompression-molding a magnet powder of a rare earth alloy or the like atan ultrahigh pressure and, thereafter, thermally treating thecompression-molded body at a high temperature (for example, 500° C. orhigher) in a vacuum furnace, so that a higher production cost is neededthan that for production of compression-bonded magnets. Also, themagnetic properties are likely to be lowered by heat treatment at a hightemperature. Further, since the binderless magnets are intended for usein a corrosive environment, it is additionally necessary to form theabove-mentioned resin coating on the surface of this rare earth magnetor to form a metal coating by electroplating or metal vapor deposition.

As the kinds of rare earth magnet powders, anisotropic magnets can beused to realize higher magnetic properties than those attained by usingisotropic magnets, but must undergo magnetic field orientation moldingby using a magnetic field molding machine. Therefore, the productioncost becomes high.

The production method of Patent Document 1 involves a separate step offorming a rust-proof thermosetting coating after formation of themagnet, and also involves repeating immersion treatment in a pluralityof times, and thus includes many production steps, provides poorproductivity, and requires a high production cost.

The present invention has been made in order to deal with such problems,and an object thereof is to provide a compression-bonded magnet with acase, which can realize high magnetic properties, high corrosionresistance and high durability strength even at low cost, and also toprovide a production method which enables production of acompression-bonded magnet with a case having such properties with highproductivity and at low cost.

Means for Solving the Problem

The compression-bonded magnet with a case according to the presentinvention is a compression-bonded magnet with a case, which comprises acompression-bonded magnet including a rare earth magnet powder and aresin binder of a thermosetting resin, a case for inserting thecompression-bonded magnet, and a sealing member, and is characterizedin: that the compression-bonded magnet is formed by compression-moldinga mixture comprising the rare earth magnet powder and the resin binderinto a green compact and curing the resin binder in the green compact;that the sealing member is fixed at an insertion opening part for thecompression-bonded magnet provided in the case; and that thecompression-bonded magnet is hermetically sealed by the sealing memberand the case. The compression-bonded magnet with a case is alsocharacterized in that the rare earth magnet powder is contained in avolume ratio of 85% to 90% with respect to the entire compression-bondedmagnet. The compression-bonded magnet with a case is also characterizedin that the rare earth magnet powder is an isotropic Nd—Fe—B magnetpowder. The compression-bonded magnet with a case is also characterizedin that it is a magnet constituting a rotation angle detection sensorfor use in a corrosive environment.

The compression-bonded magnet with a case is characterized in: that thecase is made of a non-magnetic material; that the compression-bondedmagnet is in an approximately columnar shape, and is magnetized in theradial direction of the column; that the case is arranged so as to coverthe outer peripheral surface and bottom surface sides of the column; andthat the sealing member is arranged on the upper surface side of thecolumn. The compression-bonded magnet with a case is also characterizedin that the sealing member is interposed between a part of the columnupper surface side of the outer peripheral surface of thecompression-bonded magnet and the case.

The compression-bonded magnet with a case is characterized in: that thesealing member is made of a cured product of a thermosetting resin; andthat the thermosetting resin binder contained in the compression-bondedmagnet and the thermosetting resin are cured in the same step in a statewhere the compression-bonded magnet is inserted into the case.

(1) In a method for producing a compression-bonded magnet with a caseaccording to the present invention, the compression-bonded magnet with acase comprises a compression-bonded magnet including a rare earth magnetpowder and a resin binder of a thermosetting resin, a case for insertingthe compression-bonded magnet, and a sealing member, and thecompression-bonded magnet is hermetically sealed by the sealing memberand the case. The method is characterized by comprising: a green compactmolding step of compression-molding a mixture comprising the rare earthmagnet powder and the resin binder to form a green compact; a greencompact insertion step of inserting the green compact after curing ofthe resin binder or the green compact before curing of the resin binderinto the case; and a sealing step of fixing the sealing member at aninsertion opening part for the green compact provided in the case.

(2) The method for producing a compression-bonded magnet with a case ischaracterized in: that the green compact insertion step involvesinserting the green compact before curing of the resin binder into thecase; and that the sealing step involves applying a thermosetting resinwhich serves as the sealing member after curing so as to cover anon-contact part of the green compact with the case while partiallycontacting the thermosetting resin with the case, in the insertionopening part for the green compact provided in the case and curing thethermosetting resin through heat treatment at a temperature of not lowerthan the thermosetting initiation temperatures of the thermosettingresin and the resin binder, thereby forming the sealing member whilefixing the sealing member onto the case, and, at the same time, curingthe resin binder in the green compact, thereby forming thecompression-bonded magnet.

The method for producing a compression-bonded magnet with a case is alsocharacterized in that the heat treatment in the sealing step isperformed at a temperature of not higher than 200° C. and normalpressure.

The method for producing a compression-bonded magnet with a case is alsocharacterized in: that the rare earth magnet powder is an isotropicNd—Fe—B magnet powder; and that the magnet powder is contained in avolume ratio of 85% to 90% with respect to the entire compression-bondedmagnet.

The production method according to (1) is characterized in: that thecase is made of a non-magnetic material; that the green compact and thecompression-bonded magnet are in an approximately columnar shape, andare magnetized in the radial direction of the column; that the case isarranged so as to cover the outer peripheral surface and bottom surfacesides of the column; and that the sealing member is arranged on theupper surface side of the column.

The production method according to (1) and (2) is characterized in: thatthe case is made of a non-magnetic material; that the green compact andthe compression-bonded magnet are in an approximately columnar shape,and are magnetized in the radial direction of the column; that the caseis arranged so as to cover the outer peripheral surface and bottomsurface sides of the column; that the sealing member is arranged on theupper surface side of the column; that the green compact has a step partwhich is in non-contact with the case, at least in the end part on thecolumn upper surface side of its outer peripheral surface; and that thethermosetting resin is charged into the step part in the sealing step,so that a part of the sealing member is formed in the step part.

Advantageous Effect of the Invention

The compression-bonded magnet with a case according to the presentinvention comprises a compression-bonded magnet including a rare earthmagnet powder and a resin binder of a thermosetting resin, a case forinserting the compression-bonded magnet, and a sealing member, and ischaracterized in: that the compression-bonded magnet is formed bycompression-molding a mixture comprising the rare earth magnet powderand the resin binder into a green compact and curing the resin binder inthe green compact; that the sealing member is fixed at an insertionopening part for the compression-bonded magnet provided in the case; andthat the compression-bonded magnet is hermetically sealed by the sealingmember and the case. Therefore, the compression-bonded magnet with acase is inexpensive as compared with the case of using sintered magnetsand the like which require heat treatment at a high temperature. Sincethe compression-bonded magnet with a case has the sealing member fixed,by adhesion or fitting, at the insertion opening part for thecompression-bonded magnet provided in the case, the compression-bondedmagnet can be completely hermetically sealed in the case, has excellentcorrosion resistance, and can be suitably utilized even in a corrosiveenvironment in which it is in direct contact with water, oil, exhaustgas or the like. The compression-bonded magnet itself is not required tohave high durability strength by virtue of the above-mentioned sealingstructure, and thus it becomes possible to decrease the resin binderamount and increase the rare earth magnet powder amount as compared withnot only bonded magnets obtained by injection molding but also typicalcompression-bonded magnets, thereby improving the magnetic properties.Further, when the resin binder amount is decreased, thecompression-bonded magnet itself has poor durability strength. However,the compression-bonded magnet with a case has the above-mentionedsealing structure, and thus can prevent breakage of the magnet, andshows excellent durability strength as a whole.

Since the above-mentioned rare earth magnet powder is contained in avolume ratio of 85% to 90% with respect to the entire compression-bondedmagnet, the claimed compression-bonded magnet with a case has highermagnetic properties than those of conventional compression-bondedmagnets. This rare earth magnet powder is an isotropic Nd—Fe—B magnetpowder, which is an abundant resource as well as an inexpensive materialand does not require magnetic field orientation molding by means of anexpensive magnetic field molding machine, so that the reduction inproduction cost can be attained. Also, by virtue of the above-mentionedsealing structure, the compression-bonded magnet can be completelyhermetically sealed by the case and the sealing member, so that thedeterioration of magnetic properties and rusting due to corrosion can beprevented while an isotropic Nd—Fe—B magnet powder comprising easilyoxidizable iron and rare earth elements is used.

The above-mentioned case is made of a non-magnetic material, and thecompression-bonded magnet is in an approximately columnar shape and ismagnetized in the radial direction of the column. Further, the case isarranged so as to cover the outer peripheral surface and bottom surfacesides of the column, and the sealing member is arranged on the uppersurface side of the column. Therefore, the case does not adverselyaffect the magnetic properties. Also, the case does not adversely affectthe sensor sensitivity while a thicker molded body than typical coatingsis used as the sealing member.

Since the sealing member is interposed between a part of the columnupper surface side of the outer peripheral surface of theabove-mentioned compression-bonded magnet and the case, excellentadhesion strength between the case and the sealing member can beattained, so that peeling and the like can be prevented. Also, excellentcorrosive fluid barrier properties can be attained.

The above-mentioned sealing member is made of a cured product of athermosetting resin, and the thermosetting resin binder and thethermosetting resin are cured in the same step in a state where thecompression-bonded magnet is inserted into the case. Therefore, the stepof curing the compression-bonded magnet alone and conventional coatingtreatment for improvement of corrosion resistance can be deleted, andthe production steps and treatment cost can be greatly reduced ascompared with the case where these steps and treatment are carried out.

The method for producing a compression-bonded magnet with a caseaccording to the present invention is a method for producing acompression-bonded magnet with a case comprising a compression-bondedmagnet including a rare earth magnet powder and a resin binder of athermosetting resin, a case for inserting the compression-bonded magnet,and a sealing member, wherein the compression-bonded magnet ishermetically sealed by the sealing member and the case, the methodcomprising (a) a green compact molding step of compression-molding amixture comprising the rare earth magnet powder and the resin binder toform a green compact; (b) a green compact insertion step of insertingthe green compact after curing of the resin binder or the green compactbefore curing of the resin binder into the case; and (c) a sealing stepof fixing the sealing member at an insertion opening part for the greencompact provided in the case. Thus, the method can provide thecompression-bonded magnet with a case, according to the presentinvention, having excellent properties as described above.

The green compact insertion step involves inserting the green compactbefore curing of the resin binder into the case, and the sealing stepinvolves applying a thermosetting resin which serves as the sealingmember after curing so as to cover a non-contact part of the greencompact with the case while partially contacting the thermosetting resinwith the case, in the insertion opening part for the green compactprovided in the case; and curing the thermosetting resin through heattreatment at a temperature of not lower than the thermosettinginitiation temperatures of the thermosetting resin and the resin binder,thereby forming the sealing member while fixing the sealing member ontothe case, and, at the same time, curing the resin binder in the greencompact, thereby forming the compression-bonded magnet. Therefore, thecompression-bonded magnet and the sealing member can be cured in thesame step, and are not needed to be each cured singly. Further,conventional coating treatment for improvement of corrosion resistancecan be deleted. Hence, the production steps and treatment cost can begreatly deleted, thereby enabling production of a compression-bondedmagnet with a case with high productivity and at low cost.

Since a compression-bonded magnet is adopted as the magnet, the heattreatment at the time of the above-mentioned thermosetting can beperformed at a temperature, for example, of not higher than 200° C. andnormal pressure, and no heat treatment in a vacuum or at a hightemperature is needed. Therefore, the compression-bonded magnet with acase can be produced with higher productivity and at lower cost.

In a structure in which the case is made of a non-magnetic material; thegreen compact and the compression-bonded magnet are in an approximatelycolumnar shape, and are magnetized in the radial direction of thecolumn; the case is arranged so as to cover the outer peripheral surfaceand bottom surface sides of the column; and the sealing member isarranged on the upper surface side of the column, the above-mentionedgreen compact has a step part which is in non-contact with the case, atleast in the end part on the column upper surface side of its outerperipheral surface, and the thermosetting resin is charged into the steppart in the sealing step, so that a part of the sealing member is formedin the step part. Therefore, the structure has an increased adhesionarea between the case and the sealing member and excellent adhesionstrength, and peeling and the like can thus be prevented. Also,excellent corrosive fluid barrier properties can be attained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 includes a plan view and a cross sectional view, each showing oneexample of a compression-bonded magnet with a case according to thepresent invention.

FIG. 2 includes diagrams each showing directions of lines of magneticforce of the compression-bonded magnet with a case shown in FIG. 1.

FIG. 3 is a flow chart of steps for producing the compression-bondedmagnet with a case according to the present invention.

FIG. 4 shows one example of the steps for producing thecompression-bonded magnet with a case according to the presentinvention.

MODE FOR CARRYING OUT THE INVENTION

The compression-bonded magnet with a case according to the presentinvention will now be described based on FIG. 1. FIG. 1 includes a planview (FIG. 1(a)) and a cross sectional view (FIG. 1(b)), each showing acompression-bonded magnet with a case. As shown in FIG. 1, acompression-bonded magnet with a case 1 comprises a compression-bondedmagnet 2 obtained by compression-molding a mixture comprising a rareearth magnet powder and a resin binder, and a case 3 for inserting thecompression-bonded magnet 2. A sealing member 4 is fixed at an insertionopening part 3 a for the compression-bonded magnet provided in the case3, and the compression-bonded magnet 2 is sealed by the sealing member 4and the case 3. The case 3 is in an approximately cylindrical shapehaving one opened end surface (insertion opening part 3 a) and alsohaving a constant outer diameter thickness.

The compression-bonded magnet 2 is in an approximately columnar shapehaving an approximately circular cross section which is vertical to theaxis, is inserted (press-fitted) into the case 3, and is closelycontacted with the inner wall surface of the case 3. Thecompression-bonded magnet 2 is magnetized in the radial direction of thecolumn. Specifically, the compression-bonded magnet 2 is magnetized tothe N pole on one side thereof and to the S pole on the other sidethereof, when viewed from the center of the radial direction. Here, FIG.2 schematically shows the directions of lines of magnetic force, withregard to the magnetized state of magnetic fields. As shown in FIG. 2,magnetic fields are formed in an arc shape on a plane vertical to theaxis (FIG. 2(a)) and on a vertical plane passing through the axis (FIG.2(b)). The compression-bonded magnet with a case 1 is fixed on a part ofa substance to be rotation-detected, and rotates together with thesubstance to be rotation-detected. A detection sensor 5 such as an MRsensor is arranged above the compression-bonded magnet with a case 1.Upon rotation of the compression-bonded magnet with a case 1, theintensity of magnetic field to be detected by the detection sensor 5varies depending on the rotation angle, and the detection sensor 5detects the rotation angle based on the amount of this change. Thedetection sensor 5 and the compression-bonded magnet with a case 1constitute a detection part of a rotation angle sensor.

In the present invention, a magnet comprising a rare earth magnet powderin a volume ratio of 85% to 90% with respect to the entirecompression-bonded magnet is preferably used as the compression-bondedmagnet. In this case, the resin binder is contained in a volume ratio ofabout 3% to 10%, and the porosity is about 5% to 10%. These volumeratios are volume proportions of the rare earth magnet powder and theresin binder in the final compression-bonded magnet obtained throughcompression-molding of these materials (green compact molding) andcuring of the resin binder by heat treatment, and are determined byadjusting the weights of the respective materials to be incorporated inconsideration of the specific gravities of the respective materials,molding pressure during compression-molding, porosity and the like.Incidentally, conventional compression-bonded magnets comprise a magnetpowder in a volume proportion of at most about 83% as described above,typically 75% to 80%, and have a porosity of about 10% to 15%.

The proportions of the rare earth magnet powder and the resin binder tobe incorporated are, for example, 0.5% by mass or more and less than 2%by mass for an epoxy resin (including a curing agent) and the remainderfor the rare earth magnet powder with respect to the total amount ofthese components. By employing this range, the volume ratio (85% to 90%)indicated by the above-mentioned suitable range can be attained.Incidentally, typical compression-bonded magnets comprise a resin binderin a proportion of 2% to 3% by mass with respect to the total amount ofthe rare earth magnet powder and the resin binder. Thiscompression-bonded magnet may comprise minor amounts of othercompounding agents such as calcium stearate and boron nitride, forexample, for the purpose of improving the compression moldability.

The rare earth magnet powder is contained in a volume proportion of 85%by volume or more with respect to the entire compression-bonded magnet,whereby high magnetic properties can be obtained. The “high magneticproperties” are specifically excellent maximum energy product, residualmagnetic flux density, coercive force and the like. When the rare earthmagnet powder is contained in a proportion of less than 85% by volumewith respect to the entire compression-bonded magnet, there is apossibility that the desired magnetic properties may not be obtained. Onthe other hand, when the rare earth magnet powder is contained in aproportion of exceeding 90% by volume, the resin binder amountproportionally becomes too low, resulting, for example, in a possibilitythat the case may be broken when the compression-bonded magnet ispress-fitted into the case. The rare earth magnet powder is morepreferably contained in a volume ratio of 85% to 88% with respect to theentire compression-bonded magnet. By employing this suitable range, bothof the magnetic properties and the material strength can be obtained,thereby providing the advantageous effect of compatibility withautomated press-fitting of the compression-bonded magnet into the case.

Any magnet powders can be used as the rare earth magnet powder formingthe compression-bonded magnet 2 so long as they can be adopted toproduce a rare earth permanent magnet, and examples thereof includeNd—Fe—B-based, Sm—Co-based and other magnet powders. Both of isotropicand anisotropic magnet powders can be used. Among the above-indicatedmagnet powders, an Nd—Fe—B magnet powder is preferably used because themagnet powder is made of a material which is abundant as a resource andinexpensive, and has high magnetic properties. An isotropic Nd—Fe—Bmagnet powder is particularly preferably used since the magnet powderdoes not require magnetic field orientation molding by means of amagnetic field molding machine and can realize improved productivity anda reduced production cost. Here, the isotropic Nd—Fe—B magnet powderused in the present invention has the following contents of therespective components: 27% to 40% by weight for Nd, 60% to 70% by weightfor Fe, and 1% to 2% by weight for B, and may comprise other elementsincluding Dy, Tb, Co, Cu, Al, Si, Ga, Nb, V, Pr, Mo, Zr, Ta, Ti, W, Ag,Bi, Zn and Mg in small amounts in order to improve the magneticproperties.

The compression-bonded magnet including a rare earth magnet powder(especially, Nd—Fe—B magnet powder) comprises easily-oxidizable iron andrare earth elements, and thus is likely to cause deterioration ofmagnetic properties and rusting due to oxidation corrosion when used ina corrosive environment in a state where its surface is exposed. In thepresent invention, the compression-bonded magnet is used in a statewhere it is completely hermetically sealed by the case and the sealingmember, and thus this corrosion problem can be avoided.

The average particle diameter of the rare earth magnet powder(measurement value by laser analysis method) is preferably 300 μm orless, more preferably 30 μm to 250 μm. In order to reduce void partsamong the particles after compression molding, the grain sizedistribution preferably has two peaks.

A thermosetting resin is used as the resin binder forming thecompression-bonded magnet. Examples of the thermosetting resin includeepoxy resins, phenol resins, urea resins and unsaturated polyesterresins which are known resin binders for compression-bonded magnets.Among these resins, epoxy resins are preferably used. Also, resinshaving a curing temperature which is similar to that of the resin usedin the sealing member as will be described later are preferably used.For mixing of the rare earth magnet powder and the resin binder, a drymethod or wet method can appropriately be selected depending on the typeof thermosetting resin.

Any epoxy resins may be used as the resin binder so long as they can beused for adhesion, and resins having a softening temperature of 100° to120° C. are preferred. For example, there are preferred epoxy resinswhich are solid (powder) at room temperature, but become pasty at 50° to60° C., become flowable at 130° to 140° C., and start to cause a curingreaction when further continuously heated. This curing reaction startsalso at around 120° C., but the temperature at which the curing reactionfinishes within a practical curing time, for example, 2 hours preferablyranges from 170° to 190° C. Within this temperature range, the curingtime ranges from 45 to 80 minutes. Such an epoxy resin (including alatent epoxy curing agent) and a rare earth magnet powder are dry-mixedat a temperature of not lower than the softening temperature of theepoxy resin and lower than the thermosetting initiation temperature, sothat the uncured epoxy resin can be uniformly coated onto the rare earthmagnet powder before compression molding.

Examples of the resin component of the epoxy resin used as the resinbinder include bisphenol A-type epoxy resins, bisphenol F-type epoxyresins, bisphenol S-type epoxy resins, hydrogenated bisphenol A-typeepoxy resins, hydrogenated bisphenol F-type epoxy resins, stilbene typeepoxy resins, triazine backbone-containing epoxy resins, fluorenebackbone-containing epoxy resins, alicyclic epoxy resins, novolac typeepoxy resins, acryl epoxy resins, glycidyl amine type epoxy resins,triphenol phenol methane type epoxy resins, alkyl-modifiedtriphenolmethane type epoxy resins, biphenyl type epoxy resins,dicyclopentadiene backbone-containing epoxy resins, naphthalenebackbone-containing epoxy resins and arylalkylene type epoxy resins.

The curing agent component of the epoxy resin used as the resin binderis preferably a latent epoxy curing agent. Examples of the latent epoxycuring agent include dicyandiamides, boron trifluoride-amine complexesand organic acid hydrazides. Also, a curing promoter such as tertiaryamine, imidazole or aromatic amine can be contained together with thelatent epoxy curing agent. By using the latent epoxy curing agent, it ispossible to set the softening temperature to 100° to 120° C. and thecuring temperature to 170° to 190° C., and also to establish a statewhere the rare earth magnet powder is coated with the epoxy resin(uncured), and, thereafter, to perform compression molding andthermosetting.

The rare earth magnet powder and the resin binder are mixed to form amixture, and this mixture is compression-molded, thereby forming a greencompact. For compression molding (green compact molding), a methodcomprising charging the above-mentioned mixture into a mold andpress-molding the mixture at a predetermined molding pressure can beemployed. Any mold may be used in the green compact molding step so longas a molding pressure of 490 to 980 MPa can be applied thereto.Thereafter, the resin binder in the green compact is cured through heattreatment to bind the rare earth magnet powder by means of the resinbinder. The heat treatment is performed at a temperature of not lowerthan the thermosetting initiation temperature of the resin binder (forexample, 170° to 190° C. and not higher than 200° C.) for a time duringwhich curing sufficiently proceeds (for example, 45 to 80 minutes). Whena compression-bonded magnet is preliminarily completed before insertionthereof into the case, the resin binder may be cured by adjusting thetemperature of the mold for compression molding within theabove-specified range.

While machining such as cutting or barreling can be applied, accordingto need, after thermosetting by heat treatment, the compression-bondedmagnet exhibits less shrink due to heat treatment as compared withsintered magnets. Therefore, the cost for the machining can be reduced.The magnet according to the present invention has not undergone heattreatment at a high temperature (for example, not lower than 500° C.)such as sintering, and thus can maintain high magnetic propertieswithout causing deterioration of magnetic properties in the productionsteps, and the production cost can also be reduced.

When the resin binder and the sealing member are cured in the same step,the above-mentioned green compact molding step is performed at atemperature lower than the thermosetting initiation temperature of theresin binder. In this case, the green compact of the compression-bondedmagnet is in a state of being sealed by the sealing member (beforecuring) and the case, and thus heat treatment for curing can beperformed in the air. Incidentally, when the compression-bonded magnetis preliminarily completed before insertion thereof into the case, heattreatment is performed in a vacuum atmosphere or an inert gas atmospheresuch as nitrogen gas, in order to prevent, for example, oxidativedeterioration of the rare earth magnet powder in the green compact. Whenthe epoxy resin (uncured), which is the resin binder, is coated onto therare earth magnet powder before compression molding, as described above,the rare earth magnet powder and the epoxy resin powder are introduced,for example, into a kneader to dry-mix (knead) them at a temperature of100° to 120° C. After mixing, the resultant aggregate cake is cooled,pulverized, and then charged into the mold for compression molding andheat treatment, as described above.

The resultant green compact (before curing of the resin binder) orfinished product of compression-bonded magnet is inserted into the case.For insertion of the compression-bonded magnet into the case, it ispreferably press-fitted so that the case and the compression-bondedmagnet can be closely contacted with each other. Any adhesive may beapplied between the case and the compression-bonded magnet.

The material for the case 3 is not particularly limited, but ispreferably a non-magnetic material because the material does notadversely affect the magnetic properties. In this form, thecompression-bonded magnet 2 is in an approximately columnar shape, andis magnetized in the radial direction of the column, and the case 3 isarranged so as to cover the outer peripheral surface and bottom surfacesides of the column. Therefore, the lines of magnetic force are in ashape as shown in FIG. 2. The case 3 which covers the outer peripheralsurface side of the compression-bonded magnet is made of a non-magneticmaterial, so that the lines of magnetic force from thecompression-bonded magnet are not shut off, thereby making it possibleto prevent the deterioration in magnetic properties.

Examples of the non-magnetic material for the case include resinmaterials, rubber materials and stainless non-magnetic materials such asaustenite-based materials. The stainless non-magnetic materials areclassified into sintered parts and cut products. Sintered parts arebeneficial from the viewpoints of heat resistance, dimensional accuracy,mass productivity and cost, and cut products are beneficial from theviewpoints of heat resistance, dimensional accuracy and strength. When astainless cut product or the like is used, its surface to be contactedwith a sealing member made of a thermosetting resin adhesive or aninjection-molded body of resin may be subjected to blasting such as shotsandblasting, machining (surface roughening) or drug solution treatmentwith an acid or the like, in order to improve the adhesion to thesealing member. A rubber material or resin material, when employed,provides high flexibility in shape design, and, for example, a fittingstructure which serves as a stopper after curing of the resin can beeasily formed on the case side. Incidentally, the case made of astainless non-magnetic material or the like is generally expensive andpoor in cuttability. Therefore, the case portion preferably has a simpleshape and a minimum size which allows the case to hold thecompression-bonded magnet, and is connected to a tip end of a commonmagnetic material shaft or the like.

The sealing member 4 is separate from the case 3, as shown in FIG. 1,and is fixed onto the case 3 after insertion of the compression-bondedmagnet 2 into the case 3. The sealing member 4 is in an approximatelyflat disk shape along the insertion opening part 3 a provided in thecase 3, has a thickness (X) of 0.1 mm or more, and is different fromrust-proof coating films by conventional coating. The material for thesealing member is not particularly limited so long as thecompression-bonded magnet can be sealed in the case, and any materialsincluding resin materials and metal materials can be employed. As themeans for fixing the sealing member 4 onto the case 3, adhesivefixation, press-fitting fixation, shape fitting fixation by means of ahooking structure, and the like can be adopted depending on the materialfor or structure of the sealing member 4.

In this form, the compression-bonded magnet 2 is in an approximatelycolumnar shape, and is magnetized in the radial direction of the column,the case 3 is arranged so as to cover the outer peripheral surface andbottom surface sides of the column, and the sealing member 4 is arrangedon the upper surface side of the column, as described above. Due to thisstructure, the lines of magnetic force are in a shape as shown in FIG.2, and the detection sensor 5 is arranged above the compression-bondedmagnet. Due to this shape of the lines of magnetic force, the detectionsensor 5 is not made quite adjacent to the magnet surface, but mountedwith a gap. The sealing member 4 is a thicker molded body than typicalcoatings, but can be arranged within this gap range, and thus would notadversely affect, for example, the sensor sensitivity. In order toattain stable adhesion and high corrosion resistance, the thickness (X)of the sealing member 4 preferably ranges from 0.3 mm to 1.0 mm.

The sealing member 4 is preferably made of a resin (resin molded body).Preferable resin molded bodies are those obtained by applying athermosetting resin adhesive into a thick film and curing the resinadhesive film. No separate adhesive is needed to fix the sealing memberonto the case, and the sealing member can be directly fixed by its ownadhesion force. The sealing member also has excellent adhesion to thecompression-bonded magnet. Further, the thermosetting temperature rangeis matched with the temperature range of the resin binder (thermosettingresin) contained in the compression-bonded magnet, so that the resinbinder in the compression-bonded magnet and the sealing member can becured by single treatment in the same step. This allows simplificationof production steps and reduction in production cost. Additionally, thesurface of the sealing member made of a resin may be machined, accordingto need, after resin application to form a coating and curing.

A preferable structure is such that the sealing member 4 is interposedbetween a part of the column upper surface side of the outer peripheralsurface of the compression-bonded magnet 2 and the case 3. This providesa large bonding area between the case 3 and the sealing member 4 at theedge of the insertion opening part 3 a and excellent adhesion strengthand corrosive fluid barrier properties. In the structure shown in FIG.1(b), the column height of the compression-bonded magnet 2 is loweredmore than the height of the insertion opening part 3 a (this differenceconstitutes a thickness (X)), and, further, the step part 2 a toward theinner diameter side is preliminarily provided in a part of the columnupper surface side of the outer peripheral surface of thecompression-bonded magnet 2 during compression molding (the axial lengthof this step part 2 a constitutes a thickness (Z), and the radial lengththereof constitutes a thickness (Y)). The compression-bonded magnet 2having this shape is press-fitted into the case 3, and the thermosettingresin adhesive is applied up to the edge of the insertion opening part 3a and thermoset, thereby providing a sealing member 4 which has astructure having the above-mentioned thicknesses (X), (Y) and (Z) and isin an approximately flat disk shape with a flange part. The step part 2a of the compression-bonded magnet 2 serves as a resin pool in theformation of the sealing member of a resin molded body.

The thickness (Y) of the flange part of the sealing member 4 ispreferably defined as being equivalent to the thickness (X) of the mainbody part, for example, about ±20%. The thickness (Z) of the flange partof the sealing member 4 is preferably defined within the range of twiceas large as the thickness (X) of the main body part to the height of theinsertion opening part 3 a. More preferably, the thickness (Z) is twiceto four times as large as the thickness (X) of the main body part.

Examples of the thermosetting resin adhesive used in the sealing memberinclude epoxy resin adhesives, phenol resin adhesives and acrylic resinadhesives which are excellent in heat resistance and corrosionresistance. As the epoxy resin, there can be used one-component ortwo-component epoxy resin adhesives having a resin component similar tothat of the resins listed as the above-mentioned resin binder andcapable of being diluted with a solvent. Also, amine-based curingagents, polyamide-based curing agents, acid anhydride-based curingagents and the like can also be appropriately used, in addition to theabove-mentioned latent epoxy curing agents, as the curing agent in thisepoxy resin adhesive. The curing temperature range and curing time arepreferably defined as being similar to those for the above-mentionedresin binder. There can be used phenol resin adhesives in which anovolac type phenol resin or a resole type phenol resin used as theresin component and hexamethylenetetramine or the like used as thecuring agent are dissolved in a solvent such as methyl ethyl ketone.

The thermosetting resin adhesive is used not for sealing the pores ofthe green compact, but as a thick-film sealing member, and thuspreferably has higher viscosity than that of the adhesive for poresealing treatment. Specifically, the viscosity (mPa·s) at 25° C.preferably ranges from 100 to 20000 mPa·s, more preferably ranges from500 to 10000 mPa·s. The viscosity is defined within this range, therebyproviding excellent adhesion between the case and the magnet. Also, itis possible to suppress the amount of the adhesive penetrating into thevoids of the magnet which is a green compact and to easily form asealing member having the desired film thickness on the surface of themagnet. Known methods such as spray coating and dispenser coating can beemployed for applying the thermosetting resin adhesive onto the magnetsurface. Highly-viscous adhesives can be used, and dispenser coating ispreferably employed because this method can easily realize thick filmformation and also can eliminate the waste of coating materials.

The member to which the uncured thermosetting resin adhesive has beenapplied is subjected to heat treatment to cure the adhesive. The heattreatment is performed at a temperature of not lower than thethermosetting initiation temperature of the thermosetting resin adhesive(for example, 170° to 190° C. and not higher than 200° C.) for a timeduring which curing sufficiently proceeds (for example, 1 hour) in astate where the member is put in a dryer or the like. For simplificationof production steps and the like, the curing temperature range andcuring time are matched with those for the above-mentioned resin binder,and the resin binder contained in the compression-bonded magnet and thesealing member are preferably cured at the same time in this step.

There may be an embodiment in which the case into which thecompression-bonded magnet has been inserted is arranged within the moldand the sealing member is provided thereon by injection molding (insertmolding) of a resin composition. For example, thermoplastic resins whichcan be injection-molded can be used as the resin. Examples of suchthermoplastic resins include polyolefin resins such as polyethyleneresins and polypropylene resins, polyphenylene sulfide (PPS) resins,liquid crystal polymers, polyether ether ketone (PEEK) resins, polyimideresins, polyether imide resins, polyacetal resins, polyether sulfoneresins, polycarbonate resins, polyethylene terephthalate resins,polybutylene terephthalate resins, polyphenylene oxide resins,polyphthalamide resins, polyamide resins or mixtures thereof. Amongthese resins, PPS resins or PEEK resins which are excellent in corrosionresistance and heat resistance are preferred. Also, this resincomposition may comprise any compounding agent within such a range asnot to deteriorate the function as the sealing member. Known method,conditions and mold for injection molding can be employed depending onthe kind of resin.

Additionally, when a sealing member made of a resin molded body isprovided, a structure which serves as a stopper after curing of theresin is preferably provided on the case side.

A method for producing the compression-bonded magnet with a caseaccording to the present invention will now be described based on FIGS.3 and 4. FIG. 3 is a flow chart of steps for producing thecompression-bonded magnet with a case according to the presentinvention. FIG. 4 shows one specific example of the production steps.The method for producing the compression-bonded magnet with a caseaccording to the present invention is a method for producing acompression-bonded magnet with a case comprising a compression-bondedmagnet including a rare earth magnet powder and a resin binder of athermosetting resin, a case for inserting the compression-bonded magnet,and a sealing member, wherein the compression-bonded magnet ishermetically sealed by the sealing member and the case.

This production method comprises at least three steps, specifically, agreen compact molding step (a) of compression-molding a mixturecomprising the rare earth magnet powder and the resin binder to form agreen compact; a green compact insertion step (b) of inserting the greencompact after curing of the resin binder (finished product as thecompression-bonded magnet) or the green compact before curing of theresin binder into the case; and a sealing step (c) of fixing the sealingmember at an insertion opening part for the green compact provided inthe case. FIGS. 3 and 4 show the case where the compression-bondedmagnet and the sealing member made of a thermosetting resin are cured atthe same time in the sealing step (c) and this step includes anapplication step (c1) and a thermosetting step (c2) as specificprocedures for fixing the sealing member. The respective steps will bedescribed below.

[(a) Green Compact Molding Step]

A mixture comprising a rare earth magnet powder and a resin binder iscompression-molded. For example, the mixture of the rare earth magnetpowder and the resin binder is put in a die 6 as shown in FIG. 4(a), andis compressed by an upper punch 7 and a lower punch 8 to form a greencompact 2′ (before curing). For mixing of the rare earth magnet powderand the resin binder, a dry method or wet method can appropriately beselected depending on the type of thermosetting resin of the resinbinder. For example, mixing is performed by using a mixer such as ablender or a kneader. The molding mold, rare earth magnet powder, resinbinder, curing agent component of the resin binder, etc., which are usedin this production method, are as described above.

For example, the case where a latent epoxy curing agent is used as thecuring agent component of the epoxy resin used as the resin binder isdescribed. In this green compact molding step, firstly, the rare earthmagnet powder and the epoxy resin which is the resin binder arethoroughly mixed at room temperature by means of a blender or the like.Then, the resultant mixture is introduced into a mixer such as a kneaderto be heated and mixed at the softening temperature (100° to 120° C.) ofthe epoxy resin. This heating/mixing step brings a state where theuncured epoxy resin is uniformly coated (covered) onto the surface ofthe rare earth magnet powder. Since the content heated and mixed bymeans of the mixer such as a kneader is in an aggregated cake-likeshape, this aggregate cake is pulverized at room temperature, forexample, by a Henschel mixer and sieved, thereby providing a rare earthmagnet powder whose surface is coated with the epoxy resin (uncured)which is the resin binder. A mixture of the rare earth magnet powder andthe resin binder in such a state is compression-molded to form a greencompact. This makes it possible to reduce the segregation of the magnetpowder and resin binder powder which are different in specific gravityand to improve the compressibility at the time of green compact moldingand the durability of the magnet itself as compared with the case wherethe rare earth magnet powder and the resin binder powder are simplymixed, even when the resin binder amount is smaller than usual.

[(b) Green Compact Insertion Step]

The green compact obtained in the green compact molding step is insertedinto the case, as shown in FIG. 4(b). For insertion of thecompression-bonded magnet into the case, it is preferably press-fittedso that the case and the compression-bonded magnet can be closelycontacted with each other. Any adhesive may be applied between the caseand the compression-bonded magnet.

[(c) Sealing Step—(c1) Application Step]

In the insertion opening part for the green compact provided in thecase, a thermosetting resin which serves as the sealing member aftercuring is applied so as to cover a non-contact part of the green compactwith the case while the thermosetting resin is partially contacted withthe case. Specifically, as shown in FIG. 4(c), after insertion orpress-fitting of the green compact 2′ into the case, the thermosettingresin adhesive is applied from the insertion opening part side of thecase 3 by using a dispenser, thereby providing a member in a state wherean uncured sealing member 4′ is applied to the case 3 and the greencompact 2′.

The thermosetting resin adhesive is used as a material for the sealingmember, and the thermosetting temperature range thereof is matched withthe temperature range of the resin binder (thermosetting resin)contained in the compression-bonded magnet, so that the curing (c2-1) ofthe resin binder contained in the compression-bonded magnet and thecuring (c2-2) of the sealing member can be performed simultaneouslythrough single treatment (c2) in the sealing step. Additionally, thesurface of the sealing member made of a resin may be machined, accordingto need, after resin application to form a coating and curing.

[(c) Sealing Step—(c2) Thermosetting Step]

The member in a state where the uncured thermosetting resin adhesive hasbeen applied is subjected to heat treatment to cure the adhesive (c2-2).As shown in FIG. 4(d), the heat treatment is performed at a temperatureof not lower than the thermosetting initiation temperatures of the resinbinder contained in the green compact and the thermosetting resinadhesive (for example, 170° to 190° C. and not higher than 200° C.) andnormal pressure for a time during which curing sufficiently proceeds ina state where the member is put in a dryer 10. The curing temperatureranges and curing times of the resin binder contained in the greencompact and the thermosetting resin adhesive are matched depending, forexample, on the materials selected therefor. The temperature of notlower than thermosetting initiation temperatures of the resin binder andthe thermosetting resin adhesive is not higher than 200° C., forexample, 170° to 190° C. The time during which curing sufficientlyproceeds is, for example, 45 to 80 minutes.

By virtue of this, the resin binder contained in the green compact iscured, and the rare earth magnet powder is bound by the binder to formthe compression-bonded magnet 2 (c2-1). At the same time, the sealingmember 4 is cured and formed while it is fixed onto the case 3 and thecompression-bonded magnet 2 (c2-2), thereby providing acompression-bonded magnet with a case comprising the compression-bondedmagnet 2, case 3 and sealing member 4 which are integrally formed.Finally, the compression-bonded magnet 2 is magnetized in the radialdirection, thereby forming a finished product.

In the embodiment described based on FIGS. 3 and 4 above, the step ofcuring the compression-bonded magnet and the step of curing the sealingstep can be performed in the same step, thereby making it possible togreatly reduce the production steps and the treatment cost, and toproduce a compression-bonded magnet with high productivity and at lowcost. Also, the heat treatment in the sealing step can be carried out ata temperature of not higher than 200° C. and normal pressure (in theair), and no heat treatment in a vacuum or at a high temperature isneeded. Therefore, the compression-bonded magnet with a case can beproduced with higher productivity and at lower cost.

As another embodiment of the compression-bonded magnet in the greencompact insertion step, the resin binder contained in the green compactmay also be cured to complete the compression-bonded magnet beforeinsertion thereof into the case. As an additional embodiment of thesealing member in the sealing step, the sealing member may also bepreliminarily provided as a molded body which is made of a metal orresin and is separate from the case, and fixed onto this case afterinsertion of the green compact (or compression-bonded magnet) into thecase. Further, there may be an embodiment in which the case into whichthe green compact (or the compression-bonded magnet) has been insertedis arranged within the mold and the sealing member is provided thereonby injection molding (insert molding) of a resin composition, asdescribed above.

INDUSTRIAL APPLICABILITY

The compression-bonded magnet with a case according to the presentinvention can realize high magnetic properties, high corrosionresistance and high durability strength even at low cost, and thus canbe utilized as a sensor magnet of angle detection sensors for use invarious fields including automobile field and industrial machine field.Especially, it can be suitably utilized as a sensor magnet for sensorsused in a corrosive environment in which they are in contact with afluid such as water, oil or exhaustive gas and are required to havecorrosion resistance, for example, rotation angle detection sensors inflow channel switching valves for cooling water, oil pumpopening/closing angle detection sensors and opening/closing angledetection sensors for fuel pumps.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

-   1. Compression-bonded magnet with case-   2. Compression-bonded magnet-   2′. Green compact-   3. Case-   4. Sealing member-   4′. Uncured sealing member-   5. Detection sensor-   6. Die-   7. Upper punch-   8. Lower punch-   9. Dispenser-   10. Dryer

The invention claimed is:
 1. A compression-bonded magnet with a case,comprising a compression-bonded magnet including a rare earth magnetpowder and a resin binder of a thermosetting resin, a case for insertingthe compression-bonded magnet, and a sealing member, wherein thecompression-bonded magnet is formed by compression-molding a mixturecomprising the rare earth magnet powder and the resin binder into agreen compact and curing the resin binder contained in the greencompact, the sealing member is fixed at an insertion opening part forthe compression-bonded magnet provided in the case, and thecompression-bonded magnet is hermetically sealed by the sealing memberand the case, the sealing member is made of a cured product of athermosetting resin, and the resin binder and the sealing member arecured in the same step in a state where the green compact is insertedinto the case.
 2. The compression-bonded magnet with a case according toclaim 1, wherein the rare earth magnet powder is contained in a volumeratio of 85% to 90% with respect to the entire compression-bondedmagnet.
 3. The compression-bonded magnet with a case according to claim1, wherein the rare earth magnet powder is an isotropic Nd—Fe—B magnetpowder.
 4. The compression-bonded magnet with a case according to claim1, wherein the case is made of a non-magnetic material, thecompression-bonded magnet is in an approximately columnar shape, and ismagnetized in the radial direction of the column, the case is arrangedso as to cover the outer peripheral surface and bottom surface sides ofthe column, and the sealing member is arranged on the upper surface sideof the column.
 5. The compression-bonded magnet with a case according toclaim 4, wherein the sealing member is interposed between a part of thecolumn upper surface side of the outer peripheral surface of thecompression-bonded magnet and the case.
 6. The compression-bonded magnetwith a case according to claim 1, which is a magnet constituting arotation angle detection sensor for use in a corrosive environment.
 7. Amethod for producing a compression-bonded magnet with a case comprisinga compression-bonded magnet including a rare earth magnet powder and aresin binder of a thermosetting resin, a case for inserting thecompression-bonded magnet, and a sealing member, wherein thecompression-bonded magnet is hermetically sealed by the sealing memberand the case, the method comprising: a green compact molding step ofcompression-molding a mixture comprising the rare earth magnet powderand the resin binder to form a green compact; a green compact insertionstep of inserting the green compact after curing of the resin binder orthe green compact before curing of the resin binder into the case; and asealing step of fixing the sealing member at an insertion opening partfor the green compact provided in the case, wherein the green compactinsertion step involves inserting the green compact before curing of theresin binder into the case, and the sealing step involves: applying athermosetting resin which serves as the sealing member after curing soas to cover a non-contact part of the green compact with the case whilepartially contacting the thermosetting resin with the case, in theinsertion opening part for the green compact provided in the case; andcuring the thermosetting resin through heat treatment at a temperatureof not lower than the thermosetting initiating temperatures of thethermosetting resin and the resin binder, thereby forming the sealingmember while fixing the sealing member onto the case, and, at the sametime, curing the resin binder contained in the green compact, therebyforming the compression molded-magnet.
 8. The method for producing acompression-bonded magnet with a case according to claim 7, wherein thecase is made of a non-magnetic material, the green compact and thecompression-bonded magnet are in an approximately columnar shape, andare magnetized in the radial direction of the column, the case isarranged so as to cover the outer peripheral surface and bottom surfacesides of the column, and the sealing member is arranged on the uppersurface side of the column.
 9. The method for producing acompression-bonded magnet with a case according to claim 7, wherein thecase is made of a non-magnetic material, the green compact and thecompression-bonded magnet are in an approximately columnar shape, andare magnetized in the radial direction of the column, the case isarranged so as to cover the outer peripheral surface and bottom surfacesides of the column, the sealing member is arranged on the upper surfaceside of the column, the green compact has a step part which is innon-contact with the case, at least in the end part on the column uppersurface side of its outer peripheral surface, and the thermosettingresin is charged into the step part in the sealing step, so that a partof the sealing member is formed in the step part.
 10. The method forproducing a compression-bonded magnet with a case according to claim 7,wherein the heat treatment in the sealing step is performed at atemperature of not higher than 200° C. and normal pressure.
 11. Themethod for producing a compression-bonded magnet with a case accordingto claim 7, wherein the rare earth magnet powder is an isotropic Nd—Fe—Bmagnet powder, and the magnet powder is contained in a volume ratio of85% to 90% with respect to the entire compression-bonded magnet.